Reading Rabbi Salanter article "The Study of G-d-fearing and Mussar", Yirah is translated as fear, e.g. "The fear of G-d is the forces of all man's interactions between him and G-d.". Is the translation of yirah as fear the translator's choice or did Rabbi Salanter mean fear rather then awe or fear/awe?
To actually translate, I would say it's that feeling of enormity that both fear and awe have in common.
As for the Ramchal's three types of yir'ah, I believe he places fear of punishment outside the actual middah. That yir'ah means an awareness of G-d's Enormity and Significance, which comes in two aspects (corresponding to Caution and Alacrity) -- fear of wronging Him, and awe of His Infinity.
Rabbi Micha Berger